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<script>
    var str = 'abcdacbabcbababcbabcabd'
    var arr = str.split("")
    console.log(arr);
    var res = arr.reduce(function (pre, cur) {
        if (cur in pre) {
            pre[cur] += 1
        } else {
            pre[cur] = 1
        }
        return pre
    },{})
    for(var key in res){
        console.log(key+':'+res[key])
    }
</script>